Aluminum accumulation at nuclei of cells in the root tip. Fluorescence detection using lumogallion and confocal laser scanning microscopy

The mechanistic basis for Al toxicity effects on root growth is still a mat ter of speculation, but it almost certainly involves decreased cell divisio n at the root apex. In this series of experiments, we attempt to determine whether Al enters meristematic cells and binds to nuclei when roots are exp osed to a low Al3+ activity in solution. The methodology involved the use o f the Al-sensitive stain lumogallion (3-[2,4 dihydroxyphenylazo]-2-hydroxy- 5-chlorobenzene sulfonic acid), the DNA stain 4',6-diamino-phenylindole, an d confocal laser scanning microscopy. Soybean (Glycine max L. Merr.) cv You ng (Al-sensitive) and PI 416937 (AI-tolerant) genotypes were exposed to 1.4 5 mu M Al3+ for periods ranging from 30 min to 72 h, and then washed with 1 0 mM citrate to remove apoplastic Al. Fluorescence images show that within 30 min Al entered cells of the sensitive genotype and accumulated at nuclei in the meristematic region of the root tip. Substantial Al also was presen t at the cell periphery. The images indicated that the Al-tolerant genotype accumulated lower amounts of Al in meristematic and differentiating cells of the root tip and their cell walls. Collectively, the results support an important role for exclusion in Al tolerance.